Dura-Line Smooth Wall HDPE Innerduct Conduit. All Dura-Line's smooth wall conduit meets or exceeds one or more of the following standards: ASTM F-2160, ASTM D-3035, ASTM D-2239, ASTM D-3485, NEMA TC-7, UL 651, UL 1990, Bellcore GR-356. Flexible HDPE makes gradual bends without special tools or equipment. Options include multiple SDR ratings (including SDR 13.5), a variety of colors (including orange), and factory pre-installed pull tape options (including 1250#). Co-extruded SILICORE® ULF lining is available for extended pulling performance.